Roundovers: How much do you need?

[doug20]

i used the largest router bit i could, 32mm (1 1/4") radius:

An externally hosted image should be here but it was not working when we last tested it.

which seemed to help a bit with the top end, here is the EQ'd waveguide response, (no smoothing) at 7.5deg intervals off axis. (70 deg guide)

An externally hosted image should be here but it was not working when we last tested it.

Very cool speakers!! What is that waveguide?

Im also using 1 1/4" round over on my latest build. I will have comparisons between it and the 3/4" round over in a month or so.

 

[doug20]

It's wavelength dependent. These worked out well for me in a DIY cabinet. I used 2" and it is quite large. They have 3 and 4 as well.

Aitwood Anderson International - StoreFront


Rob

Thanks Rob, I have seen that site before. They have some great choices. I wish I was closer to one though to save on shipping costs.

 

[buggsson]

Accidently, the last couple of days I've spent quite a few hours reading up on the subject of diffraction, both types. When rounding the baffle edges is useful differ quite a bit. That they are frequency dependent seem to be agreed, but if I understood the authors correct, the radii had to be from one wavelength down to 1/4 wavelength to do any real good (authors would be Linkwitz, D'Appolito and Dickason). Even if this were to be correct, then even a 1/4 wavelength would get us quite high up in frequency before being of use?

And to use beveled edges, Dickason's results from his tests in LCD 7ed, there have to be some quite substantial bevels to be effective.

I'm still, after all the reading done, as much confused as before, about how to deal with the problems, except that mounting the driver/s non centrally on the baffle, and maybe to put some foam on the baffle surface.

 

[HK26147]

That they are frequency dependent seem to be agreed,

Yes.
John Murray in this:
True Audio TechTopics: Diffraction Loss
Examined the 24" sphere of Olson's and came up with a formula

Careful inspection of Olson's spherical diffraction loss curve reveals a -3dB frequency of about 190 Hz for the 24" sphere. Assuming that the 3 dB frequency is inversely proportional to the baffle diameter I have arrived at the following approximation for calculating the -3dB frequency as a function of baffle diameter.
f(3) = 380/W(B)
(where W(B) is the baffle width in feet)

Sanity Check: for Olson's 24" (2 feet) baffle we calculate f(3) = 380/2 = 190 Hz . . .OK!

Not content with the use of a fixed term 380 in that equation...

24" in terms of wavelength is approx 570Hz.
1/3 of that wavelength = 190Hz which corresponds to -3db point.
( The 1/3 wavelength relationship can be translated to a phase relationship of 120 degrees. )

True Audio Speaker Topics: Spatial Loading
If a driver is in-wall that is much closer to Half Space = 2 pi steradians.
A driver on a baffle goes from half space to full space until it encounters objects and boundaries.